The lower olefins (for example, ethylene, propylene, butylene, butadiene and C4 derivatives) and aromatics (for example, benzene, toluene and the xylenes) are basic and essential intermediates which are widely used in the petrochemical and chemical industries. Thermal cracking, or steam pyrolysis, is a major type of process for forming these materials, typically in the presence of steam and in the absence of oxygen. Feedstocks for pyrolysis can include petroleum gases and distillates such as naphtha, kerosene, and gas oil. However, the availability of these feedstocks is usually limited and requires costly and energy-intensive process steps in a crude oil refinery.
Studies have been conducted using heavy hydrocarbons as a feedstock for steam pyrolysis reactors. A major drawback in conventional heavy hydrocarbon steam pyrolysis operations is coke formation.
In addition, the yields and distributions of olefins and aromatics using heavy hydrocarbons as a feedstock for a steam pyrolysis reactor are different than those using light hydrocarbon feedstocks. Heavy hydrocarbons have a greater content of aromatics and a higher boiling point than light hydrocarbons. Greater aromaticity may be indicated by a greater Bureau of Mines Correlation Index (BMCI). BMCI is a measurement of aromaticity of a feedstock and is calculated as follows:BMCI=87552/VAPB+473.5*(sp. gr.)−456.8  (1)where:VAPB=Volume Average Boiling Point in degrees Rankine andsp. gr.=specific gravity of the feedstock.
As the BMCI decreases, ethylene yields are expected to increase. Therefore, highly paraffinic or low aromatic feeds are usually used for steam pyrolysis to obtain greater yields of desired olefins and to avoid greater yields of undesirable products and coke formation in the reactor coil section. In light of this boiling point differential, the specification may also utilize higher boiling point fraction when referring to heavy hydrocarbons and lower boiling point fraction when referring to light hydrocarbons.
To be able to respond to the growing demand of these petrochemicals, other type of feeds which can be made available in larger quantities, such as crude oil, are attractive to producers. “Crude oil” is to be understood to include whole crude oil from conventional sources, as well as crude oil that has undergone some pre-treatment. The term “crude oil” is also to be understood to include crude oil that has been subjected to water-oil separation, gas-oil separation, desalting, stabilization, or combinations of such. Using crude oil feeds will minimize or eliminate the likelihood of the refinery being a bottleneck in the production of these petrochemicals. Current integrated crude conditioning steam cracking processes fail to efficiently convert the heavy fraction of the upgraded crude oil into petrochemicals, such as olefins and aromatics, and result in high levels of coke formation.